1. Field of Invention
The present invention generally relates to attachment devices for attachment of electrical or electronic devices, and more particularly to an attachment device for attachment of an electrical or electronic device to a top-hat rail.
2. Description of Related Art
In construction of equipment and installations, it is conventional to attach electrical or electronic devices, such as control and regulation devices, signal converters, and power supply units, to top-hat shaped mounting rails or top-hat rails. The electrical or electronic devices and their housings have an insertion region for such a purpose, with corresponding guide grooves or holding devices on one side of the insertion region, while on the other, opposite, side of the insertion region there is a movable, spring-pretensioned, bolt with one or two attachment hooks. Instead of forming guide grooves and the spring-loaded bolt directly on the housing of the device, use of a separate carrier plate attached or screwed to the housing can be employed.
There are several requirements with respect to attachment of such devices to the top-hat rail. First of all, it is often desirable for the device to be easily removable from the top-hat rail. For this purpose, in known attachment devices, the spring-loaded bolts generally have an actuation opening for insertion of a screwdriver so that the bolt can be pulled back against the spring force of the springs and thus the device can be removed from the top-hat rail. At the same time, the spring-loaded bolts ensure that the attachment device cannot unintentionally detach or be removed from the mounting rails.
German Patent Application No. DE 80 01 902 U1 discloses an electrical switching device for seating on a top-hat rail, wherein on its housing on one side of the insertion region there being a stationary guide groove and on the other, opposite, side of the insertion region there being a movable bolt with an attachment hook. The bolt or slide, which is located in a guide groove made in the housing bottom, has two guide bridges, which are vertically offset on the long side, and which in their middle region are provided on the inside at a distance and parallel to one another with opposite elastic lever arms. Because the bolt or slider is produced in one piece from elastic plastic, the use of a separate spring need not be employed.
German Patent Application No. DE 10 2005 028 841 B4 discloses an electrical switching device, which can be locked onto a mounting rail by a stationary projection being formed on the bottom of the housing facing the mounting rail, and additionally by a second attachment projection being implemented by a movable slide located in a guide groove in the housing. The slide in addition to the second attachment projection has a spring rod, which is supported in the housing in the mounted state of the slide. The spring rod being made on the side of the slide opposite the second attachment projection results in that the second attachment projection can be located in the vicinity of one face side of the switching device so that the attachment device is located highly decentralized with respect to the back of the housing and thus the switching device can also be attached to the mounting rail when the installation space is greatly limited on the end side.
German Patent Application No. DE 20 2005 010 601 U1 discloses a modular cap housing for seating on a mounting rail, the housing having a locking means with two locking slides, which can be moved relative to one another, and which are integrally interconnected via a spring. The two locking slides each have hook-shaped sections for extending under the edges of the mounting rail, the sections of the two locking slides being arranged opposite one another. So that the housing can be lifted off the mounting rail, there is provided a rotating spreading pin, which can push the two locking slides apart against the force of the springs.
An attachment device having a carrier plate made from a sheet metal part and with a clip device, which has a slide, is described in German Patent Application No. DE 94 06 386 U. In such attachment device, the clip device in addition to the U-shaped slide also has a helical compression spring, which has a spring force that pushes the end-side catch projections of the slide to under the second edge of the top-hat rail. To guide the helical compression spring, the slide has a holding crosspiece with the helical compression spring in the tensioned state being clamped between a cross leg, which has been made on the slide, and a stop angle, which is bent on the carrier plate.
However, even if such a known attachment device already fundamentally enables very reliable mounting of even larger electrical devices, it still has some disadvantages. For example, such a known attachment device employs a helical compression spring of a small size, which constitutes a separate component that must first be mounted on the slide, and that can be easily lost during installation. Moreover, the helical compression spring in the mounted state has only a relatively small spring force, since the spring constant of a helical compression spring can only be chosen to be so large that the spring can be compressed by the user with reasonable force in order to release the electrical device from the top-hat rail. The force which is necessary for pulling back the slide is in any case greater than the spring force with which the catch projections of the slide are pressed to under the second edge of the top-hat rail.